Inorganic membrane reactors configuration

Zaspalis and Burggraaf [47] have summarized typical membrane reactor configurations, different membrane/ catalyst combinations, and a large number of membrane reactor studies. Their article clearly shows that inorganic membranes prepared by the sol-gel method, with their dual ability in catalysis and separation, have many unique advantages over other product forms. At the same time, it is important to realize that the parameters which affect a membrane s characteristics and the advantages which the sol-gel process offers are similar to what has been presented thus far. 

When implemented in the field, inorganic membrane reactors invariably will be large in scale and complex in configuration. Their reliable design and operation rest on the foundation of good understanding and design of laboratory and pilot reactors. An important tool that helps build that foundation is validated mathematical models. 

In addition to the above conventional configurations, there have been some novel designs proposed for various typxjs of inorganic membrane reactors. They will be discussed here. 

Before proceeding further it would be appropriate for our readers to familiarize themselves with the few additional acronyms that will be used in this chapter and which are listed in Table 11.1. They are used to describe some of the most common membrane reactor configurations that have been studied in the technical literature. By far the most commonly referred to reactor is the PBMR, in which the reaction function is provided by a packed bed of catalysts in contact with the membrane. The membrane is not itself catalytic at least not intentionally so. Some of the commonly utilized inorganic and metal membranes, on the other hand, are intrinsically catal) ically active. The PBMR clcissification, therefore, should be assigned with caution. When the packed bed... 

The increasing interest in inorganic membranes for gas applications is undoubtedly due to their excellent high temperature resistance. Inorganic membrane reactors (including carbon membranes) may thus have a very nice potential for industrial applications. The various configurations of membrane reactors will however not be discussed in the current chapter. Their separation properties may be understood on the basis of the materials used, kinetics, and process conditions. 

Ilias and Govind(lO) have reviewed the development of high temperature membranes lor membrane reactor application. Hsieh(4) has summarized the technology in the area of important inorganic membranes, the thermal and mechanical stabilities of these membranes, selective permeabilities, catalyst impregnation, membrane/reaction considerations, reactor configuration, and reaction coupling. 

Besides the application of inorganic membranes in stand-alone gas separation units, attention is focused on more process-integrated applications. In such configurations the separation hmction of the membrane can be used to shift the equilibrium of a chemical reaction by selective removal of one or more components on the product side of the reaction in a so-Ccdled membrane reactor. 

Immobilization is the process of adhering biocatalysts (isolated enzymes or whole cells) to a solid support. The solid support can be an organic or inorganic material, such as derivatized cellulose or glass, ceramics, metallic oxides, and a membrane. Immobilized biocatalysts offer several potential advantages over soluble biocatalysts, such as easier separation of the biocatalysts from the products, higher stability of the biocatalyst, and more flexible reactor configurations. In addition, there is no need for continuous replacement of the biocatalysts. As a result, immobilized biocatalysts are now employed in many biocatalytic processes. 

Figure S.4S Configuration of a tubular inorganic catalytic membrane reactor module (Cent et al., 2003).

The variety of porous membranes, in terms of both materials and microstructures, makes them popular in different chemical reaction processes. They are applied mostly in a tubular configuration. However, the hollow fiber represents a trend for future development due to its remarkably high area/volume ratio. Table 2.5 summarizes the conventional inorganic porous membranes used in membrane reactors. 

One of them employs membrane-based separation processes connected to the esterification reaction. In this respect, vapor permeation and pervaporation process have been tested and dn-ee different layouts have been reported for ethyl lactate production. In one of them, membrane module is located outside the reactor unit and the retenate is recirculated to the reactor." " In another scheme, the membrane module is placed inside the reactor, but the membrane does not participate in the reaction directly and simply acts as a filter," " and in the third configuration, membrane itself participates in die reaction catalysis (catalytic membrane reactor)." Different hydrophilic membranes, such as polymeric, ceramic, zeolites and organic-inorganic hybrid membranes were tested. ... 

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